That web page is literally 34 words of text, with no images and a small two line CSS file. It isn't going to empty your data plan, unless you are using a 300 baud modem :-)

The problem is that people can only know it after going there, and risking (with what 90% certainty?) emptying their plan.

Sounds like visiting HN is a risk to them then. The whole point of HN is to provide links to interesting sites.

And the person visited the website who gave the summary. Presumably they already knew.